Internal combustion engines, including diesel engines, gasoline engines, gaseous fuel-powered engines, and other engines known in the art exhaust a complex mixture of air pollutants. These air pollutants are composed of gaseous compounds including, among other things, the oxides of nitrogen (NOX). Due to increased awareness of the environment, exhaust emission standards have become more stringent, and the amount of NOX emitted to the atmosphere by an engine may be regulated depending on the type of engine, size of engine, and/or class of engine.
In order to comply with the regulation of NOX, some engine manufacturers have implemented one or more strategies for dealing with emissions. One exemplary strategy is called selective catalytic reduction (SCR). SCR is an exhaust treatment process where a reductant, most commonly urea ((NH2)2CO) or a water/urea solution, is selectively injected into the exhaust gas stream of an engine and adsorbed onto a downstream catalyst. The injected urea solution decomposes into ammonia (NH3), which reacts with NOX in the exhaust gas to form water (H2O) and diatomic nitrogen (N2), which may be unregulated substances.
In some applications of SCR strategies and other exhaust treatment strategies, multiple catalysts may be required for greater emissions control requirements. However, there can be large tolerance variations amongst the catalysts, which can lead to problems with packaging multiple catalysts together. In addition, the catalysts can bulge when subject to increased temperatures during operation, and the bulging can result in additional problems when packaging multiple catalysts together. Specifically, the bulging and increased pressure can cause damage to the catalysts and make it difficult to stack and package multiple catalysts, while retaining a desired shape of the package.
One attempt to improve packaging of multiple catalysts is described in U.S. Pat. No. 4,859,428 (“the '428 patent”) to Brand et al. that was issued on Aug. 22, 1989. In particular, the '428 patent describes an apparatus for the support and containment of monolithic ceramic catalyst elements. The apparatus includes an elastic gasket attached on one or both monolith ends and a metal frame attached on the gasket under pressure. The frame has recesses on two adjacent lateral surfaces, and projections on at least two opposite lateral surfaces which can engage interlockingly into the recesses of adjacent frames.
While the apparatus of the '428 patent may help to improve packaging of multiple catalysts, it may be less than optimal. Specifically, while the gasket and metal frame of the apparatus of the '428 patent may contain a group of catalysts, the apparatus of the '428 patent does not retain each catalyst individually within the group to provide additional support and stability. Further, the apparatus of the '428 patent does not adequately retain a desired shape and size of the package, such that other packages of multiple catalysts may be stacked together.
The retention system of the present disclosure solves one or more of the problems set forth above and/or other problems with existing technologies.